Production of α-chloroisopropyl-substituted aromatics

ABSTRACT

α-Chloroisopropyl-substituted aromatics are obtained in high yield by treating isopropenyl-substituted aromatics with hydrogen chloride gas in the absence of a solvent. The α-chloroisopropyl-substituted aromatics serve as initiators for the cationic polymerization of isobutene.

The present invention relates to a process for preparingα-chloroisopropyl-substituted aromatics.

α-Chloroisopropyl-substituted aromatics, such as m- or p-dicumylchloride or 1,3,5-tricumyl chloride, served as inifer molecules forpreparing linear or star-shaped telechelic polyisobutenes. The reactionof the inifer with a Lewis acid results in a complex having 2 or 3carbocationic or cationogenic centers which can add onto isobutenemolecules. The carbocationic tert-butyl termini of the linear orstar-shaped polyisobutenes obtained may be converted to olefinic orother functional groups, cf., for example, EP-A 0 713 883.

J. P. Kennedy, L. R. Ross, J. E. Lackey, O. Nuyken, Polym. Bull. 1981,4, 67-74 describe the synthesis of 1,3,5-tris(α-chloroisopropylbenzene)by reacting 1,3,5-triisopropenylbenzene with hydrogen chloride indichloromethane at 0° C. For the workup, the dichloromethane has to bedistilled off.

On the other hand, O. Nuyken, G. Maier, D. Young, M. B. Leitner,Macromol. Chem., Macromol. Symp. 60, (1992) 57–63 disclose that1,4-diisopropenylbenzene forms a polymer having 1,1,3-trimethylindane orα-methylstyrene repeating units under the influence of Lewis or Brönstedacids.

It is an object of the present invention to provide a process by whichα-chloroisopropyl-substituted aromatics is obtained in high yield andwith simple workups.

We have found that this object is achieved by a process for preparingα-chloroisopropyl-substituted aromatics of the formula I

where n is an integer from 2 to 4 be treating isopropenyl-substitutedaromatics of the formula II

with hydrogen chloride in the absence of a solvent.

The process according to the invention allowsα-chloroisopropyl-substituted aromatics to be obtained in virtuallyquantitative yields. This is surprising to a high degree, since thoseskilled in the art would have expected a reaction in the absence of asolvent to result in the occurrence of numerous undesired secondaryreactions or the cationic polymerization of the isopropenyl-substitutedaromatics (cf. O. Nuyken et al., loc. cit.). The success of the processaccording to the invention is believed to be based on the instability ofcarbocations, from which undesired secondary reactions orpolymerizations can start, in the absence of a solvent, in particular ofa polar solvent.

The process according to the invention can be carried out in a simplemanner by passing hydrogen chloride gas through theisopropenyl-substituted aromatics or by reacting it therewith in apressure vessel. This utilizes the fact that both the reactant and theproduct of the process according to the invention are liquid at reactiontemperature and that the use of a solvent is unnecessary. The workup isgenerally limited to the removal of excess hydrogen chloride gas fromthe product, for example by stripping with inert gas such as nitrogen.Yield losses resulting from workup steps are avoided.

The process according to the invention is preferably effected at atemperature of from −10 to +50° C., in particular from 0 to 15° C., anda pressure from 1 to 10 bar. It may be carried out batchwise orcontinuously.

The reaction may optionally be accelerated by using Lewis or Brönstedacid catalysts. Useful catalysts include Lewis acids such as aluminumtrichloride, aluminum tribromide, boron trifluoride, boron trifluoridealkoxide, boron trifluoride etherate, titanium tetrachloride, tintetrachloride, ethylaluminum dichloride, iron trichloride, antimonypentachloride or antimony pentafluoride; Brönsted acids such as sulfuricacid, phosphoric acid, trifluoromethanesulfonic acid and the like.Organic protic acids may also be present in polymerically bound form,for example as ion exchanger resins.

In the formulae I and II, n is preferably 2 or 3. Preferredisopropenyl-substituted aromatics are 1,3,5-triisopropenylbenzene,1,4-diisopropenylbenzene and 1,3-diisopropenylbenzene, and particularpreference is given to the latter. Apart from the isopropenylsubstituents, the benzene ring may bear further substituents which donot impair the reaction according to the invention, in particularC₁-C₄-alkyl radicals such as methyl, ethyl or t-butyl. Useful reactantsfor the process according to the invention also include mixtures ofdifferent isopropenyl-substituted aromatic.

The isopropenyl-substituted aromatics used as reactants are known andobtainable, for example, by dehydrating α-hydroxyl-substituted aromatics(cf. DE-A 1 618 449), Wittig reaction of acetylbenzenes (cf. J. P.Kennedy et al., Polym. Bull. 1981, 4, 67–74) or by dehydrogenatingisopropylbenzenes (cf. JP-2001026558 and JP-2000327596).

The α-chloroisopropyl-substituted aromatics obtained by the processaccording to the invention can be used in a manner known per se forpreparing homopolymers of isobutene or copolymers of isobutene withvinylaromatics by living cationic polymerization. On this subject,reference is made, for example, to EP-A 0 713 883, DE-A 199 37 562 orDE-A 100 61 715.

The invention is illustrated by the examples which follow.

EXAMPLE 1

A 1 l four-necked flask was initially charged with 500 g (3.16 mol) of1,3-diisopropenylbenzene. 290 g (7.95 mol) of hydrogen chloride werepassed in within 7.5 h with cooling to an internal temperature of 5° C.and at atmospheric pressure. Unconverted HCl was then removed bystripping with nitrogen. 715 g (98%) of1,3-bis(α-chloroisopropyl)benzene remained as a colorless liquid;chlorine content 29.3%; ¹H-NMR (CD₂Cl₂, 360 MHz): 2.00 (s, 12 H,methyl), 7.29–7.52 (m, 3 H, aromat. H), 7.82–7.83 (m, 1 H, aromat. H).

EXAMPLE 2

A 500 ml four-necked flask was initially charged with 200 g (1.26 mol)of 1,3-diisopropenylbenzene. 135 g (3.70 mol) of hydrogen chloride werepassed in within 8 h with cooling to an internal temperature of 5° C.and at atmospheric pressure. Unconverted HCl was then removed underreduced pressure. 288 g (99%) of 1,3-bis(α-chloroisopropyl)benzeneremained as a colorless liquid; chlorine content 28.6%; ¹H-NMR (CD₂Cl₂,360 MHz): 2.00 (s, 12 H, methyl), 7.29–7.52 (m, 3 H, aromat. H),7.82–7.83 (m, 1 H, aromat. H).

COMPARATIVE EXAMPLE 3

A 2 l four-necked flask was initially charged with 200 g (1.26 mol) of1,3-diisopropenylbenzene in 750 ml of CH₂Cl₂ and this was then admixedwith about 1 ml of ethanol. 12.5 g (3.42 mol) of hydrogen chloride werepassed in within 7 h with cooling to an internal temperature of 5° C.and at atmospheric pressure. The solvent and also unconverted HCl wasthen removed under reduced pressure. 264 g (90%) of1,3-bis(α-chloroisopropyl)benzene remained as a colorless liquid;chlorine content 29.2%; ¹H-NMR (CD₂Cl₂, 360 MHz): 2.00 (s, 12 H,methyl), 7.29-7.52 (m, 3 H, aromat. H), 7.82-7.83 (m, 1 H, aromat. H).

EXAMPLE 4

An autoclave was initially charged with 490 g (3.10 mol) of1,3-diisopropenylbenzene. 200 g (5.6 mol) of HCl were metered in within3 h in such a manner that the internal pressure was 5 bar and theinternal temperature did not exceed 30° C. The remaining HCl was removedby stripping with nitrogen. 705 g (99%) of1,3-bis(α-chloroisopropyl)benzene were obtained as a colorless liquid;chlorine content 30.6%; ¹H-NMR (CD₂Cl₂, 360 MHz): 2.00 (s, 12 H,methyl), 7.29-7.52 (m, 3 H, aromat. H), 7,82-7,83 (m, 1 H, aromat. H).

EXAMPLE 5

A 40 l V4A steel stirred reactor was initially charged with 18.0 kg (114mol) of 1,3-diisopropenylbenzene. 10.1 kg (277 mol) of hydrogen chloridewere passed in within 8 h at an internal temperature of 5-10° C. (brinecooling) and an internal pressure of 1.1 bar. The remaining HCl wasremoved by stripping with nitrogen. 26 kg (99%) of1,3-bis(α-chloroisopropyl)benzene were obtained as a colorless liquid;chlorine content 30.1%; ¹H-NMR (CD₂Cl₂, 360 MHZ): 2.00 (s, 12 H,methyl), 7.29–7.52 (m, 3 H, aromat. H), 7.82-7.83 (m, 1 H, aromat. H).

1. A process for preparing α-chloroisopropyl-substituted aromatics ofthe formula I

where n is an integer from 2 to 4 comprising treating at least oneisopropenyl-substituted aromatic of the formula II

with hydrogen chloride in the absence of a solvent, wherein the benzenering of the isopropenyl-substituted aromatic of formula (II) mayoptionally bear one or more substituents which do not impair reaction ofsaid aromatic of formula (II) and hydrogen chloride, whereby the benzenering of the α-chloroisopropyl-substituted aromatics of the formula Iwill bear the same substituents.
 2. A process as claimed in claim 1,wherein the treatment is effected at a temperature of from −10 to 50° C.3. A process as claimed in claim 1, wherein the treatment is effected ata pressure of from 1 to 10 bar.
 4. A process as claimed in claim 1,wherein said isopropyl isopropenyl-substituted aromatic of the formulaII is 1,3-diisopropenylbenzene.
 5. A process as claimed in claim 1,wherein the treatment is accelerated by the presence of a Lewis orBrönsted acid catalyst.
 6. A process as claimed in claim 2, wherein thetreatment is effected at a temperature of from 0 to 15°C.
 7. A processas claimed in claim 1, wherein n is 2 or
 3. 8. A process as clained inclaim 1, wherein the isopropenyl-substituted aromatic of formula (II) isat least one of 1,3,5-triisopropenylbenzene, 1,4-diisopropenylbenzeneand 1,3-diisopropenylbenzene.
 9. A process as claimed in claim 1,wherein the benzene ring of the isopropenyl-substitued aromatic offormula (II) bears said one or more substituents.
 10. A process asclaimed in claim 9, wherein the substituents are selected from the groupconsisting of C₁–C₄-alkyl radicals.